Ants belonging to species of Camponotus, commonly known as carpenter ants, are an important economic pest. They cause structural damage to homes, telephone poles, and trees by tunneling into the wood. Methods to control carpenter ants have been evaluated based on effectiveness against the ants, environmental safety and ease of use, especially for pest control operators (PCO's) concerned with ant population management. Carpenter ants have been controlled in the field by use of sprays or dusts, methods that are considered by many to be environmentally unfriendly. Furthermore, exposure of the spray or dust to environmental elements may limit the effectiveness of the toxicant, for example, by rain washing it away. A "cleaner," more effective method of control is to place a toxic bait in an ant station so as to prevent exposure to non-target organisms, such as children and pets, and to shield the bait from environmental factors that may cause degradation and dilution of the toxicant. While non-particulate solid baits are potentially safer than liquids, powders or granular materials, they generally are not suitable for use in rebaitable, semi-enclosed ant stations. Typically, when such solid baits have been depleted, the entire self-contained station must be replaced. Preferred toxicants are ones that are slow enough acting to allow the ant time to bring it back to the nest a rid thereby deliver the toxicant to the rest of the colony.
Ants are selective in their preference for baits. What one species of ant finds appealing, another species may ignore. It is known that carpenter ants are particularly selective, but they may be attracted to baits that are moist and sweet. U.S. Pat. No. 3,962,461 describes honey and the insecticide Mirex in a liquid bait. The utility of this bait is limited by the need for an organic solvent to help solubilize Mirex and by its form as a liquid. Only a limited amount of solvent may be used before the carpenter ants are repelled, and as a liquid the bait is unsafe to children and pets.
Described in European Patent No. 0295 442 is a solid, non-particulate bait. This bait comprises the liquid sugars corn syrup and molasses, ground protein, and a polymeric binder. The polymeric binder is disclosed as conferring good coherency to the composition, thus providing a solid form that is safer in a household environment than liquids, powders or granular materials. The effectiveness of ground protein as an added feeding attractant depends on the time of season. Early in the season carpenter ants seek a mixture of sugar and protein; later they become more satisfied with food that consists entirely of sugars. Examples of ground protein having utility in baits include dried fish meal and silkworm pupae (EP0 295 442).
WO91/07972 describes an aqueous gel bait containing carrageenan which is reported to be an effective gelling agent. Such aqueous gels have an advantage over other bait forms in that they are pourable, albeit at temperatures above 60.degree. C. With a pourable bait, a pest control professional may prepare the bait station for either indoor or outdoor ant control. However, the need to heat the bait in order to make it pourable is an obvious limitation since the bait cannot be readily dispensed at room temperature.
A suitable toxicant is one that is both toxic to the ant at low concentrations and slow acting so that the ant will distribute the toxicant to others in the colony. Examples of toxicants reported to have utility in ant baits include fluorinated sulfonamides such as sulfluramid, C.sub.8 H.sub.17 SO.sub.2 NHC.sub.2 H, (U.S. Pat. No. 4,921,696); boric acid (WO 91/07972); vyrazolines (U.S. Pat. No. 5,196,408); diflubenzuron, a chitin synthesis inhibitor (JO 1224-307); and certain hydrazones (U.S. Pat. No. 4,087,525).
It is an object of this invention to provide a highly effective carpenter ant bait that may be dispensed into an ant station at room temperature. It is a further object of this invention to provide a bait formulation that consists almost entirely of sugars so as to have both a moist, sweet surface attractive to the ants and physical properties that yield a viscous and fluid bait that may be readily used by a pest control operator in baiting an ant station.